A hybrid animal known as a "zebroid" (horse-zebra) has been successfully used as a draft animal in South Africa, and like the more familiar.    From Wordnik.com.  [Conservapedia - Recent changes [en]] Reference

Maybe when you saw a zebroid (half donkey and / or horse with a zebra).    From Wordnik.com.  [The Boston Phoenix PHLOG] Reference

Today there are also believed to be a handful of ligers around the world and a similar number of tiglons, the product of a tiger father and lion mother. are smaller than ligers and take on more physical characteristics of the tiger. zeedonk, a cross between a zebra and a donkey; the zorse or zebroid, a zebra/horse cross; and the beefalo, an American bison/domestic cow cross.    From Wordnik.com.  [Telegraph.co.uk: news, business, sport, the Daily Telegraph newspaper, Sunday Telegraph] Reference

Given this info, on further thought it seems likely that a naturally-occurring pregnancy from a union between a zebra and another equine might give the mother’s body a chance to go into “pregnancy mode” and carry the zebroid baby to term.    From Wordnik.com.  [Zorse – The Zebra Horse Hybrid] Reference